Currently developed telecommunication technologies provide solutions for performing a handover (HO) operation from a Long Term Evolution (LTE) or High Speed Packet Access (HSPA) system to a second generation or third generation mobile network (2G/3G) under normal conditions. Such an operation often involves a handover from a Voice over Internet Protocol (VoIP) sessions using Internet Protocol Multimedia Subsystems (IMS) to a circuit switched domain, and is sometimes referred to as a single radio voice call continuity (SRVCC) operation.
In currently available SRVCC operations, a handover typically involves a mobile switching center (MSC) executing a domain transfer using a session transfer number (STN-SR). The STN-SR may be a unique number or value (such as an E.164 address) that is stored in a Home Subscriber Server (HSS) of a user. The STN-SR routes to a Service Centralization and Continuity Application Server (SCC AS) of the home network. Although telecommunication technologies provide for such handover operations under normal conditions, currently available technologies fail to provide adequate solutions for such a handover during an emergency session.
These deficiencies are due, at least in part, to the fact that the STN-SR routes to an SCC AS in the home network, whereas emergency calls or sessions are assumed to be in visited networks. Additionally, Dual-Radio Voice Call Continuity (Dual-Radio VCC) technology fails to provide a viable solution. In Dual-Radio VCC, the SCC AS returns a dynamic STN to the UE in session initiation protocol (SIP) signaling when the emergency call is established. The UE then uses the dynamic STN to execute a domain transfer. However, this solution cannot be used in an emergency SRVCC scenario because an SRVCC handover and domain transfer is triggered by the visited network, which is not aware of the dynamic STN. Accordingly, currently available telecommunication technologies fail to provide support for SRVCC emergency calls or sessions.